Quantifying Transient Soil Moisture Dynamics Using Multipoint Direct‐Current Resistivity in Homogeneous Sand

Abstract

Direct measurements of soil moisture are extremely diffi cult to obtain between the spaal scales of point measurements and remote sensing. Nevertheless, the spa otemporal distribu on of soil moisture remains a key variable in hydrology. In this study, we explored the use of mul point direct-current resis vity to examine spa otemporal changes in soil moisture following a rapid infi ltra on event into a large macropore. The methodology was selected because the me scale of fl ow processes in the homogeneous isotropic sand prevented the use of imaging techniques. Selec on of an appropriate electrode array was cri cal for collec ng the required high-resolu on spa otemporal resis vity measurements in a 1.44-m-diameter tank. Direct placement of a dense array of electrodes in the sand allowed us to use geosta s cal methods for spa al interpola on, thereby removing the inherent uncertainty resul ng from inversion mechanics (i.e., smoothness constraints for underconstrained problems). Instead, conversion of resis vity to satura on was directly performed using Archie's law. We compared the observa ons to a two-dimensional, axisymmetric, numerical solu on of the system using the HYDRUS 2D/3D so ware, and to a semianaly cal solu on to es mate soil hydraulic proper es. We found sa sfactory comparisons among the observa ons and the numerical and semianaly cal solu ons of the system, which indicates that these techniques may be applicable to fi eld-scale es mates of eff ec ve hydraulic proper es. Subject to limi ng ini al condi ons, boundary condions, and material proper es, the results of the semianaly cal solu on are encouraging for capturing general hillslope-scale dynamics at longer temporal scales toward a greater understanding of emergent pa erns in dryland ecosystems.Abbrevia ons: TDR, me domain refl ectometry.

The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso

“…When the degree of macroporosity in the soil is high, the steady state assumption might not hold. In these cases, alternative, more complex models of water flow should be used, such as dual porosity models [Gerke and Vangenuchten, 1993], models based on macropores characteristics [Leonard et al, 2004], or other alternative models [Franz et al, 2011].…”

Coupling vegetation organization patterns to soil resource heterogeneity in a central Kenyan dryland using geophysical imagery

“…On the basis of a sensitivity analysis using the CS616 and EMI images, we found a value of five for the exponent to give satisfactory fit for the unsaturated flow behavior. We note that a more rigorous analysis estimating unsaturated flow parameters using an inverse solution procedure may be performed if sufficient data are available [ Franz et al , 2011; Simunek et al , 2006].…”

Impact of the capillary fringe in vertically integrated models for CO2 storage

“…Furthermore, the materials are often chosen such that the capillary forces are weak, in accordance with the sharp interface assumption. In experiments with stronger capillary forces, the sharp interface approximation is less suited [see, e.g., Franz et al, 2011]. Similarly, numerical experiments, particularly when line symmetry is assumed, tend to show quantitative and qualitative differences between sharp interface [see, e.g., Hesse et al, 2008; Juanes et al, 2010] and resolved models (see, e.g., Riaz and Tchelepi [2006] and Pruess et al [2009] for analysis of similar problems).…”